Supersonic Debited my account 8 months after I cancelled!

Hi, I cancelled my services with your company in April/May last year. I spoke to your call center agent and they stated that everything was paid up with your company and I didn't owe anything. Your company should have call recordings of this. I returned the modem in perfect working order. I logged in to the portal after all that to see that everything was in order and it was. So please tell me why, after nearly eight months, your company has debited my account? The amount was for R1,248.99. I have not subscribed to any services with your company since I cancelled, so why am I being debited? Now my bank wants to charge me R50 for your companies mistake! Do I need to change bank accounts to make sure that your company doesn't debit me? This is just ridiculous now. Please, I just want my money back and I never want to hear from your company ever again.